The present invention relates to solar energy conversion apparatus and, more particularly, to improvements in solar energy collectors of the dish and trough reflector variety. Further, this invention relates to improvements in methods for producing both dish and trough types of reflectors.
Considerable time and effort is presently being expended in determining the feasibility of utilizing the sun's energy as a means for supplying the heating and power needs of home and industry. While there is little question that the know-how exists for converting solar energy into vast quantities of heat and electrical energy, the principle stumbling block confronting widespread commercial use of the sun's rays for such purposes is one of economics. Because of the high costs associated with the manufacture of efficient solar energy converters of a practical size, the economics still favor the use of conventional fossil fuels.
A major factor contributing to the relatively high cost of solar energy converters is the cost associated with the manufacture of the collector component, i.e. the reflector or lens which acts to collect and focus solar rays to form a region of intense heat. To produce significant quantities of heat or electrical energy from solar energy, collectors of substantial size are required. To satisfy the requirement, large dish and trough-shaped reflectors have been proposed and, in some instances, are being utilized as the collector element. While such reflectors are substantially less expensive than refractive elements of comparable light-gathering power, their manufacturing costs are, for the size required, still at a level which renders large-scale energy production economically non-feasible. To date, dish and trough reflectors have been conceived and/or made of glass, space-frame structures and segmented sheets, or molded composite plastic materials. See, for instance, the trough reflector disclosed in U.S. Pat. No. 3,841,738 to Caplan. Such conventional reflectors are not only difficult to fabricate, but also they require the use of relatively expensive materials. As a consequence, few, if any, are economically attractive.
In my U.S. Pat. No. 4,119,365, I disclose a trough reflector which, compared to previously devised structures, is considerably simpler in construction and, hence, less costly to fabricate. This trough reflector comprises a relatively flexible planar reflector supported between a pair of spaced parallel arms. The support arms are rotatably mounted on a frame, and one arm is free to slide toward and away from the other to assure that the ultimate shape of the reflector is not influenced by end loads. Rotation of the support arms in opposite directions produces a pure bending moment in the reflector, the result being that the reflector assumes a concave shape represented by a sector of a right cylinder. Such a surface has relatively good focusing properties and can be modified relatively easily toward the optimum parabolic cross-section by selectively adding small end loads to the reflector.
While the trough reflector disclosed in my U.S. Pat. No. 4,119,365 is, compared to prior art reflectors, relatively inexpensive to manufacture, it does include certain structural elements which act to produce the requisite pure bending moment in the reflector. Preferably, such structure comprises two pairs of ball bearing assemblies for rotatably supporting the support arms, a mechanical linkage by which equal and opposite torques can be applied to the support arms to produce the requisite bending moments in the reflector, and longitudinal beams to maintain structural integrity. Such components, of course, add signficantly to the overall manufacturing costs of the trough reflector and should, if possible, be eliminated.